I read that :The theoretical maximum length of Unique loop is 16.Unique Rectangle type has 1, 2, 3 and 4.BUG type also has 1, 2, 3 and 4,BUG type 3 nearly always occurs with a BUG type 4,it is frequent enough to find Sudoku requiring both a BUG type 4 and a BUG type 1.

So I have these questions:Why the maximum length of Unique loop can't over 16?Are there puzzles have to require all of BUG types ( from 1 to 4 ) ?Are there puzzles have to require all of Unique Rectangle types ( from 1 to 4 ) ?

I find one has Unique Rectangle types 1 and Unique Rectangle types 4........4..716..2...12.9....8..1...26.....3.1...69..8.......9.545..268......3....

Here's a puzzle with UR Types 1, 2, 3, and 4. Note I look for Type 3 before Type 4 and all may not be necessary, but I think the idea here is to have some fun and not be necessarily to be to strict. It also contains an 7-cell XY-chain.

Mike Barker wrote:Here's a puzzle with UR Types 1, 2, 3, and 4. Note I look for Type 3 before Type 4 and all may not be necessary, but I think the idea here is to have some fun and not be necessarily to be to strict. It also contains an 7-cell XY-chain.